Centrifugal fans



Sep'f, 1960 J. D. MURPHY 2,951,630

CENTRIFUGAL FANS Filed Aug. so, 1957 VOLUME d'owaza Patented Sept. 6, 1960 .fic

CENTRIFUGAL FANS James i). Murphy, Framingham, Mass., assigner to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Files Aug. se, i957, ser. N0. 631,352 2 Claims. (c1. 23o- 114) This invention relates -to centrifugal fans, and has as an object to adjust the output volumes of centrifugal fans.

Centrifugal `fans are usually designed to be operated at a constant speed, and to have maximum eiciencies at their design output volumes. For many duties, it is desirable to vary the output volume of a centrifugal fan, and in the past, this has usually been accomplished by dampers or spin vanes. Darnpers are ineicient since they reduce output without reducing the power required. Spin vanes are ecient but are complicated and costly.

I have found that the output volume of a centrifugal fan having a non-shrouded, radial impeller, can be simply and efficiently varied by shifting an inlet passage towards and from the cut-off of the fan. Ordinarily, the inlet passage is axially aligned with the fan impeller. I have found that moving such an inlet passage so that it is located nearer the cutoff than it is when it is concentric with the impeller, the output volume of the fan is increased, and that moving the inlet passage so that it is located further from the cut-off than when it is concentric with the impeller, the output volume of the fan is reduced.

I have also found that by pivoting the cut-off sheet, and linking it to the inlet passage so that it is movable therewith, the output change accomplished by the movement ofthe inlet passage is increased.

My invention will now be described with reference to the annexed drawings, of which:

Fig. 1 is a side elevation of a centrifugal fan embodying my invention;

Fig. 2 is a section along the line Z--2 of Fig. l, and

Fig. 3 is a family of efficiency-volume curves showing the outputs of the fan at different positions of the inlet plate.

The illustrated fan has an impeller having a hub 11 on a rotary shaft 12. The impeller has radial blades 13 which do not have the apertured side plates usually used with fan impellers, and are, therefore, unshrouded.

The lfan has a conventional, scroll-shaped casing 14 around the impeller, and a conventional tangential outlet 15, the back edges of the blades 13 extending parallel to and being closely spaced from the back wall 16 of the casing. The shaftV 12 of the fan extends through au opening in the wall 16.

The casing has a front wall 17 with an opening 18 facing the impeller 10, and has secured thereto above and below the opening .18 by bolts 19, plates 20 that have horizontally extending slots 21 therein. An inlet conduit 22 formed to provide a convergent-divergent inlet passage 23, has an out-turned outer Wall with a circular outer edge 35 clamped to the insides of the plates 20 by bolts 24'extendng -through the slots 21. The bolts 24 have wing-nuts 25 thereon. The conduit 22 is slidable horizontally within the opening 18.

The fan has a eut-off where the scroll-shaped casing 14 starts, with a cut-off sheet 26 pivoted at 27 to the interior of the casing at the cut-olf. The sheet 26 is connected to the inlet conduit 22 by linkage 28, the latter being pivoted to the sheet 26 and to the plate 22.

Opposite to the cut-off, the inlet conduit 22 has pivoted thereto one end of an arm 30, the other end of which is pivoted to a pivoted lever 31 which has an indicator 32 opposite to a calibrated scale 33.

Normally, the inlet conduit 22 would be positioned so that its edge 35 and the passage 23 would be concentric with the impeller 10 in the positions 35C and 23C respectively, shown by Fig. l, and with the cut-olf sheet in the position 26C shown by Fig. l. In these positions of the inlet passage and the cut-off sheet, the fan would have the characteristic curve C of Fig, 3.

When the lever 31 is adjusted to move the inlet conduit 22 so as to place its edge 35 and the inlet passage 23 towards the cutoff to the positions 35A and 23A respectively, and the cut-off sheet to the position 26A shown by Fig. 1, the fan would have the characteristic curve A of Fig. 3. This curve A shows by comparison with the curve C of Fig. 3, that the operating point of the fan has been moved to provide a greater output volume without any change in efficiency.

When the lever 31 is adjusted to move the inlet conduit 22 to place its `edge 35 and the inlet passage 23 away from the cut-off to the positions 35B and 23B respectively, and the cut-01T sheet in the position 26B shown by Fig. 1, the fan would have the characteristic curve B of Fig. 3. This curve shows by comparison with curve C of Fig. 3 that the operating point of the fan has been moved to provide a smaller output volume without any change in etliciency.

The scale 33 would be calibrated to show output volumes.

A single size fan can be made to perform the duties of several sizes of fans, at the time of manufacture, by properly locating the gas inlet passage of the fan to suit the load as described in the foregoing.

What I claim is:

1. A centrifugal fan comprising an impeller having a non-shrouded inlet side, a scroll-shaped casing around said impeller, said casing having a cutof adjacent to the perimeter of said impeller, the side of said casing opposite and adjacent to said impeller inlet side having an opening therein, a conduit having an inlet passage concentric with said impeller at one position of said conduit, and means for slidably supporting said conduit to said casing side adjacent to said opening in said casing side.

2. A centrifugal -fan comprising an impeller having a non-shrouded inlet side, a scroll-shaped casing around said impeller, said casing having a cut-off adjacent to the perimeter of said impeller, a cut-off sheet pivoted to said casing at said cut-off, the side of said casing opposite and adjacent to said impeller side having an opening therein, a conduit having an inlet passage concentric with said impeller at one position of said conduit, means for slidably supporting said conduit to said casing side adjacent to said opening in said casing side, and means connecting said sheet and conduit for moving said sheet in the direction of movement of said conduit.

References Cited in the tile of this patent UNITED STATES PATENTS 820,398 Davidson May 15, 19016 820,399 Davidson May l5, 1906 1,862,523 Anderson June 14, 1932 2,205,902 McMahan June 25, 1940 2,452,274 Walters Oct. 26, 1948 2,635,548 Brawley Apr. 2l, 1953 2,767,905 Creed Oct. 23, 1956 2,798,657 Darrow July 9, 1957 FOREIGN PATENTS 1,326 Great Britain of 1911 542,597 France May 19, 1922 1,068,014 France Feb. 3, 1954 

